Recently, optical detectors and waveguides have garnered increased attention for a variety of applications. One application is the transmission of information on computer chips. The trend is toward using wavelength division multiplexing (WDM) to transmit data in an optical system. WDM is a technology which multiplexes multiple optical carrier signals on a single optical fiber by using different wavelengths, i.e., different colors of light, to carry different signals. This allows for a multiplication in capacity, in addition to making it possible to perform bidirectional communications over one strand of fiber. Optical detectors that may be used for WDM systems have the ability to sense the presence of light. However, conventional optical detectors are generally wavelength insensitive for radiation with photon energy exceeding bandgap, or the energy difference between the top of the valence band and the bottom of the conduction band for the same electron quasimomentum. Thus, due to the limitations of conventional optical detectors and other components of the conventional optical transmission system, such as modulators, nano-wavelengths of light may not be used for the transmission of information.
One form of optical detectors, Schottky barrier detectors, typically include a semiconductor, such as silicon, or any III-V material such as GaAs, InP, AlGaAs, InGaAsP, GaN, InGaN, with an over-lying Schottky electrode. The interface between the semiconductor and the Schottky electrode is known as the Schottky energy barrier. In a Schottky detector, electron-hole pairs are generated in the semiconductor by the incident photons when light impinges onto the detector. As the electron-hole pairs are swept from the semiconductor by a built-in field that is reverse-biased, a photo current is generated in the external circuit. Therefore, while Schottky detectors can detect light that has a photon energy above bandgap, they are generally wavelength insensitive for above bandgap radiation. That is, they lack the ability to detect particular wavelengths of light. Instead, they only provide an indication that light is present, without determining which wavelength of the light is present.
While Schottky barrier detectors have been employed successfully as optical detectors, they are not wavelength selective. Conventional optical detectors, including Schottky barrier detectors, suffer from several other drawbacks as well. First, conventional optical detectors incorporating wavelength selectivity are relatively difficult to fabricate; the wavelength selectivity is usually accomplished by the addition of interference filters that require tens to hundreds of nanometers of precision dielectric or semiconductor layers. This is a very limiting factor in applications where space is a premium or the need for low cost, such as applications for computer chips. Second, the fabrication of conventional optical detectors and waveguides is a very complex process. Fabricating these structures requires excessive time and expense.